title: A novel oral tracer procedure for measurement of habitual myofibrillar protein synthesis.
abstract: BACKGROUND
  Conventionally, myofibrillar protein synthesis is measured over time periods of hours. In clinical studies, interventions occur over weeks. Functional measures over such periods may be more representative. We aimed to develop a novel method to determine myofibrillar protein fractional synthetic rate (FSR) to estimate habitual rates, while avoiding intravenous tracer infusions.
  
  
  METHODS
  Four healthy males were given 100 g water enriched to 70 Atom % with (2)H2O as a single oral bolus. Vastus-lateralis needle biopsies were performed and plasma samples collected, 3-13 days post-dose. (2)H enrichment in body water was measured in plasma using continuous flow isotope ratio mass spectrometry (IRMS). Myofibrillar protein was isolated from muscle biopsies and acid hydrolysed. (2)H enrichment of protein-bound and plasma-free alanine was measured by gas chromatography (GC)/pyrolysis/IRMS. Myofibrillar protein FSR was calculated (% day(-1)).
  
  
  RESULTS
  The tracer bolus raised the initial enrichment of body water to 1514 ppm (2)H excess. Water elimination followed a simple exponential. The average elimination half-time was 8.3 days. Plasma alanine, labelled during de novo synthesis, followed the same elimination kinetics as water. The weighted average myofibrillar protein FSR from the four subjects was 1.38 % day(-1) (range, 1.0-1.9 % day(-1) ).
  
  
  CONCLUSIONS
  Myofibrillar protein FSR was measured in free-living healthy individuals over 3-13 days. Using a single oral (2)H2O bolus, endogenous labelling of alanine occurred in a predictable manner giving estimates of synthesis comparable with published values. Furthermore, the protocol does not compromise the ability to measure other important metabolic processes such as total energy expenditure.
authors.affiliation: Clinical and Surgical Sciences, University of Edinburgh, The Chancellor's Building, 49 Little France Crescent, Edinburgh, EH16 4SB, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: MacDonald
authors.forename: A C
authors.initials: AC
authors.lastname: Small
authors.forename: C A
authors.initials: CA
authors.lastname: Greig
authors.forename: H
authors.initials: H
authors.lastname: Husi
authors.forename: J A
authors.initials: JA
authors.lastname: Ross
authors.forename: N A
authors.initials: NA
authors.lastname: Stephens
authors.forename: K C H
authors.initials: KC
authors.lastname: Fearon
authors.forename: T
authors.initials: T
authors.lastname: Preston
mesh_terms: D000328:Adult; D002849:Chromatography, Gas / Q000379:methods*; D006801:Humans; D007700:Kinetics; D008297:Male; D013058:Mass Spectrometry / Q000379:methods*; D009124:Muscle Proteins / Q000097:blood / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018482:Muscle, Skeletal / Q000737:chemistry / Q000378:metabolism; D009210:Myofibrils / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014176:Protein Biosynthesis
chemical_list: D009124:Muscle Proteins